#include<stdio.h>
long n,k,i,j;
int a[2000001];
int main(){

freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);

scanf("%ld",&n);

for(i=2;i<=n;i++)
    if(a[i]==0)
    {
    for(j=2*i;;j=j+i)if(j<n)a[j]=1;
    k++;
    }

printf("%ld",k);
return 0;
}